The present invention relates generally to methods and apparatus for treating ischemic heart disease, and more particularly, cases involving diffuse coronary atherosclerosis, by perfusing the myocardium with oxygenated blood from the left ventricle using the coronary venous vasculature.
The cardiac blood perfusion system is composed of two coronary arterial vessels, the left and right coronary arteries, which perfuse the myocardium from the epicardial surface inward towards the endocardium. Blood flows through the capillary systems into the coronary veins, and into the right atrium via the coronary sinus. Two additional systems, the lymphatic and the Thebesian veins, drain a portion of the blood perfused into the myocardium directly into the heart chambers. The venous system has extensive collaterals and, unlike the coronary arteries, does not occlude in atherosclerotic disease.
A number of techniques have been developed to treat ischemic heart disease caused, for example, by atherosclerosis. These treatments have improved the lives of millions of patients worldwide, yet for certain classes of patients current technology offers little relief or hope.
Best known of the current techniques is coronary artery bypass grafting, wherein a thoracotomy is performed to expose the patient""s heart, and one or more coronary arteries are replaced with saphenous veins. In preparation for the bypass grafting, the heart is arrested using a suitable cardioplegia solution, while the patient is placed on cardiopulmonary bypass (i.e., a heart-lung machine) to maintain circulation throughout the body during the operation. Typically, a state of hypothermia is induced in the heart muscle during the bypass operation to reduce oxygen utilization, thereby preserving the tissue from further necrosis. Alternatively, the heart may be perfused throughout the operation using either normal or retrograde flow through the coronary sinus, with or without hypothermia. Once the bypass grafts are implanted, the heart is resuscitated, and the patient is removed from cardiopulmonary bypass.
Drawbacks of conventional open heart surgery are that such surgery is time-consuming and costly, involves a significant risk of mortality, requires a lengthy period of recuperation, and involves significant discomfort to the patient.
As a result of the foregoing drawbacks, techniques have been developed that permit coronary bypass grafting to be performed endoscopically, i.e., using elongated instruments inserted through incisions located between the ribs. A drawback of these keyhole techniques, however, is that they can be used only for coronary arteries that are readily accessible, and not, for example, those located posteriorly.
Alternatively, techniques such as percutaneous transluminal angioplasty (xe2x80x9cPTAxe2x80x9d) have been developed for reopening arteries, such as the coronary arteries, that have become constricted by plaque. In these techniques, a balloon catheter is typically inserted into the stenosis and then inflated to compress and crack the plaque lining the vessel, thereby restoring patency to the vessel. Additionally, a vascular prosthesis, commonly referred to as a xe2x80x9cstent,xe2x80x9d may be inserted transluminally and expanded within the vessel after the angioplasty procedure, to maintain the patency of the vessel after the PTA procedure.
U.S. Pat. No. 5,409,019 to Wilk describes an alternative method of creating a coronary bypass, wherein a valve-like stent is implanted within an opening formed between a coronary artery and the left ventricle. The patent describes that the stent may be implanted transluminally.
A drawback of the foregoing transluminal approaches is that the treatment device, e.g., the balloon catheter or the stent delivery system described in U.S. Pat. No. 5,409,019, must be inserted in the vessel before it can be expanded. Occasionally, a stenosis may occlude so much of a vessel that there is insufficient clearance to advance a guidewire and catheter within the stenosis to permit treatment. In addition, arterial blockages treatable using PTA techniques are restricted to the portions of the anatomy where such techniques can be beneficially employed.
Moreover, the above-described techniquesxe2x80x94both openxe2x80x94surgery and transluminalxe2x80x94are useful only where the stenosis is localized, so that the bypass graft or PTA procedure, when completed, will restore near normal blood flow to the effected areas. For certain conditions, however, such as diffuse atherosclerosis, blockages may exist throughout much of the coronary artery system. In such situations, treatment, if possible, typically involves heart transplant.
Historically, attempts have been made to treat diffuse blockages of the coronary arterial system by introducing retrograde flow through the coronary venous system. As described, for example, in W. Mohl, xe2x80x9cCoronary Sinus Interventions: From Concept to Clinics,xe2x80x9d J. Cardiac Sura., Vol. 2, pp. 467-493 (1987), coronary venous bypass grafts have been attempted wherein the coronary sinus was ligated, and a shunt was implanted between a cardiac vein and the aorta, thus providing permanent retrograde perfusion. It was observed that such bypass grafts resulted in underperfusion of certain regions of the myocardium and edema of the venous system. Consequently, as reported in the aforementioned Mohl article, these techniques are rarely used in cardiac surgery, while permanent retroperfusion is never used in interventional cardiology.
Despite disenchantment with retroperfusion via the coronary sinus for long-term perfusion of the myocardium, retrograde coronary venous perfusion is now routinely used in coronary interventional procedures to perfuse the heart during the procedure. Franz et al., in xe2x80x9cTransfemoral Balloon Occlusion of the Coronary Sinus in Patients with Angina Pectoris,xe2x80x9d Radiologia Diagnostica, 31(1), pp. 35-41 (1990), demonstrated the possibility of transfemoral coronary sinus balloon occlusion in patients with angina pectoris. In recent years, the use of retrograde arterial perfusion of blood through the coronary sinus has gained wide acceptance as a technique to preserve the myocardium during bypass procedures (Kuraoka et al., xe2x80x9cAntegrade or Retrograde Blood Cardioplegic Method: Comparison of Post-Surgical Right Ventricular Function and Conduction Disturbances,xe2x80x9d Japanese J. Thoracic Surg., 48(5), pp. 383-6, (1995)) and during high risk or complicated angioplasty (Lincoff et al., xe2x80x9cPercutaneous Support Devices for High Risk or Complicated Coronary Angioplasty,xe2x80x9d J. Am. Coll. Cardiol., 17(3), pp. 770-780 (1991)). This perfusion technique allows continuous warm cardioplegia and allows the flow of blood through the coronary venous bed distal to the occlusion.
It has also been reported by Rudis et al. in xe2x80x9cCoronary Sinus Ostial Occlusion During Retrograde Delivery of Cardioplegic Solution Significantly Improves Cardioplegic Distribution and Efficiency,xe2x80x9d J. Thoracic and Cardiovasc. Surg., 109(5), pp. 941-946 (1995), that retrograde blood flow through the coronary venous system may be augmented by coronary ostial occlusion. In this case, blood flows retrograde to the myocardium and drainage is through the lymphatic system and the Thebesian veins. Huang et al., in xe2x80x9cCoronary Sinus Pressure and Arterial Venting Do Not Affect Retrograde Cardioplegic Distribution,xe2x80x9d Annals Thoracin Surg., 58(5), pp. 1499-1504, that flow through the myocardium is not significantly effected by coronary arterial occlusion and venting, or by increases in coronary perfusion pressure. Also, K. Ihnken et al., in xe2x80x9cSimultaneous Arterial and Coronary Sinus Cardioplegic Perfusion, an Experimental and Clinical Study,xe2x80x9d Thoracic and Cardiovascular Surgeon, Vol. 42, pp.141-147 (June 1994), demonstrated the benefits of using simultaneous arterial and coronary sinus perfusion during cardiac bypass surgery, with no ventricular edema, lactate production, lipid peroxidation, or effect on post-bypass left ventricular elastance or stroke work index.
For a large number of patients in the later phases of ischemic heart disease, and particularly diffuse atherosclerotic disease, current technology offers little relief or hope. In such instances, humanely extending the patient""s life for additional months may provide significant physical and emotional benefits for the patient.
In view of the foregoing, it would be desirable to provide methods and apparatus for treating ischemic heart disease in a wider range of open surgical and interventional cardiology procedures.
It also would be desirable to provide methods and apparatus for providing transvenous myocardial perfusion that reduce the risk of edema within the venous system.
It would further be desirable to provide methods and apparatus that enable patients suffering from the later phases of diffuse ischemic heart disease to experience renewed vigor, reduced pain and improved emotional well-being during the final months or years of their lives.
In view of the foregoing, it is an object of this invention to provide methods and apparatus for treating ischemic heart disease in a wider range of open surgical and interventional cardiology procedures.
It is another object of the present invention to provide methods and apparatus for providing transvenous myocardial perfusion that reduce the risk of edema within the venous system.
It is a further object of this invention to provide methods and apparatus that enable patients suffering from the later phases of diffuse ischemic heart disease to experience renewed vigor, reduced pain and improved emotional well-being during the final months or years of their lives, or which provides critical time during which a donor heart, for example, may be located for transplantation.
In accordance with the present invention, methods and apparatus are provided for forming one or more passageways or conduits between the left ventricle and the coronary venous vasculature (hereinafter referred to a xe2x80x9cveno-ventricular passagewaysxe2x80x9d), thereby supplying long-term retrograde perfusion of the myocardium.
A first embodiment of the apparatus, suitable for use in percutaneous applications, is advanced through the coronary ostium (in the right atrium) and positioned within a selected portion of the venous vasculature. Access to the right atrium may be established using either the subclavian veins and the superior vena cava or an approach through a femoral vein. Once one or more passageways of suitable size are formed between the left ventricle and selected portions of the venous system using the apparatus of the present invention. The coronary ostium is then partially or fully occluded with a plug or valve constructed in accordance with the present invention.
In accordance with the methods of the present invention, the degree of occlusion of the coronary ostium is selected to provide adequate back-pressure in the venous system, so that blood flowing into the venous system from the left ventricle flows in a retrograde direction to perfuse the myocardium. Alternatively, or in addition, a plug may be deployed to occlude a portion of a vein upstream of the outlet of a veno-ventricular passageway, to occlude collaterals adjacent to the passageway, or both.
Further in accordance with the methods of the present invention, the apparatus provides a diameter of the passageway, or a number of veno-ventricular passageways, so that a parameter associated with the pressure attained in the venous system does not exceed a predetermined value. Alternatively, or in addition, a flow-limiting stent or valve optionally may be deployed in the veno-ventricular passageway to prevent overpressure in the venous system.
A second embodiment of the apparatus provides for formation of the veno-ventricular passageways, and implantation of support devices in those passageways, using intra-operative techniques.
Further alternative embodiments of the apparatus of the present invention comprise conduits that may be implanted either transeptally or extracorporeally. A third embodiment of apparatus comprises a conduit that includes a first end, which is inserted transeptally through the right atrium and obliquely into the posterior septal endocardium of the left ventricle via the posterior pyramidal space, and a second end which is inserted into the coronary sinus via the coronary ostium in the right atrium. The conduit may optionally include means for maintaining a parameter associated with the pressure attained in the conduit and coronary venous vasculature below a predetermined value, such as a one-way valve preventing backflow from the coronary sinus to the left ventricle during the late phases cardiac diastole.
A fourth embodiment of the invention, suitable for use in an intraoperative procedure, comprises a conduit having a first end that is affixed in communication with the left ventricle near its apex, and a second end having a plug that is inserted into the coronary ostium via an opening through the wall of the right atrium or vena cavae. In this embodiment, the mid-region of the conduit is disposed within the pericardium and may comprise an elastic material that assists in regulating the pressure of the blood flow entering the coronary sinus. The conduit may also include a tapered inlet that assists in regulating the flow.
Further features of the invention, its nature and various advantages will be more apparent from the accompanying drawings and the following detailed description of the preferred embodiments.